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doc: Move SRFI-9 records under "Compound Data Types".

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Suggested by Mark Weaver.

* doc/ref/srfi-modules.texi (SRFI-9): Keep the node, but move contents
  to...
* doc/ref/api-compound.texi (SRFI-9 Records): ...here.
  (Record Overview): New section.
This commit is contained in:
Ludovic Courtès 2012-11-10 16:02:35 +01:00
parent 3d01c19a78
commit ec7e4f77ec
2 changed files with 153 additions and 103 deletions
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152
doc/ref/api-compound.texi
View file

@ -25,8 +25,10 @@ values can be looked up within them.
* Generalized Vectors:: Treating all vector-like things uniformly.
* Arrays:: Matrices, etc.
* VLists:: Vector-like lists.
* Records::
* Structures::
* Record Overview:: Walking through the maze of record APIs.
* SRFI-9 Records:: The standard, recommended record API.
* Records:: Guile's historical record API.
* Structures:: Low-level record representation.
* Dictionary Types:: About dictionary types in general.
* Association Lists:: List-based dictionaries.
* VHashes:: VList-based dictionaries.
@ -2249,6 +2251,152 @@ Return a new vlist whose contents correspond to @var{lst}.
Return a new list whose contents match those of @var{vlist}.
@end deffn
@node Record Overview
@subsection Record Overview
@cindex record
@cindex structure
@dfn{Records}, also called @dfn{structures}, are Scheme's primary
mechanism to define new disjoint types. A @dfn{record type} defines a
list of @dfn{fields} that instances of the type consist of. This is like
C's @code{struct}.
Historically, Guile has offered several different ways to define record
types and to create records, offering different features, and making
different trade-offs. Over the years, each ``standard'' has also come
with its own new record interface, leading to a maze of record APIs.
At the highest level is SRFI-9, a high-level record interface
implemented by most Scheme implementations (@pxref{SRFI-9}). It defines
a simple and efficient syntactic abstraction of record types and their
associated type predicate, fields, and field accessors. SRFI-9 is
suitable for most uses, and this is the recommended way to create record
types in Guile. Similar high-level record APIs include SRFI-35
(@pxref{SRFI-35}) and R6RS records (@pxref{rnrs records syntactic}).
Then comes Guile's historical ``records'' API (@pxref{Records}). Record
types defined this way are first-class objects. Introspection
facilities are available, allowing users to query the list of fields or
the value of a specific field at run-time, without prior knowledge of
the type.
Finally, the common denominator of these interfaces is Guile's
@dfn{structure} API (@pxref{Structures}). Guile's structures are the
low-level building block for all other record APIs. Application writers
will normally not need to use it.
Records created with these APIs may all be pattern-matched using Guile's
standard pattern matcher (@pxref{Pattern Matching}).
@node SRFI-9 Records
@subsection SRFI-9 Records
@cindex SRFI-9
@cindex record
SRFI-9 standardizes a syntax for defining new record types and creating
predicate, constructor, and field getter and setter functions. In Guile
this is the recommended option to create new record types (@pxref{Record
Overview}). It can be used with:
@example
(use-modules (srfi srfi-9))
@end example
@deffn {library syntax} define-record-type type @* (constructor fieldname @dots{}) @* predicate @* (fieldname accessor [modifier]) @dots{}
@sp 1
Create a new record type, and make various @code{define}s for using
it. This syntax can only occur at the top-level, not nested within
some other form.
@var{type} is bound to the record type, which is as per the return
from the core @code{make-record-type}. @var{type} also provides the
name for the record, as per @code{record-type-name}.
@var{constructor} is bound to a function to be called as
@code{(@var{constructor} fieldval @dots{})} to create a new record of
this type. The arguments are initial values for the fields, one
argument for each field, in the order they appear in the
@code{define-record-type} form.
The @var{fieldname}s provide the names for the record fields, as per
the core @code{record-type-fields} etc, and are referred to in the
subsequent accessor/modifier forms.
@var{predicate} is bound to a function to be called as
@code{(@var{predicate} obj)}. It returns @code{#t} or @code{#f}
according to whether @var{obj} is a record of this type.
Each @var{accessor} is bound to a function to be called
@code{(@var{accessor} record)} to retrieve the respective field from a
@var{record}. Similarly each @var{modifier} is bound to a function to
be called @code{(@var{modifier} record val)} to set the respective
field in a @var{record}.
@end deffn
@noindent
An example will illustrate typical usage,
@example
(define-record-type employee-type
(make-employee name age salary)
employee?
(name get-employee-name)
(age get-employee-age set-employee-age)
(salary get-employee-salary set-employee-salary))
@end example
This creates a new employee data type, with name, age and salary
fields. Accessor functions are created for each field, but no
modifier function for the name (the intention in this example being
that it's established only when an employee object is created). These
can all then be used as for example,
@example
employee-type @result{} #<record-type employee-type>
(define fred (make-employee "Fred" 45 20000.00))
(employee? fred) @result{} #t
(get-employee-age fred) @result{} 45
(set-employee-salary fred 25000.00) ;; pay rise
@end example
The functions created by @code{define-record-type} are ordinary
top-level @code{define}s. They can be redefined or @code{set!} as
desired, exported from a module, etc.
@unnumberedsubsubsec Non-toplevel Record Definitions
The SRFI-9 specification explicitly disallows record definitions in a
non-toplevel context, such as inside @code{lambda} body or inside a
@var{let} block. However, Guile's implementation does not enforce that
restriction.
@unnumberedsubsubsec Custom Printers
You may use @code{set-record-type-printer!} to customize the default printing
behavior of records. This is a Guile extension and is not part of SRFI-9. It
is located in the @nicode{(srfi srfi-9 gnu)} module.
@deffn {Scheme Syntax} set-record-type-printer! name thunk
Where @var{type} corresponds to the first argument of @code{define-record-type},
and @var{thunk} is a procedure accepting two arguments, the record to print, and
an output port.
@end deffn
@noindent
This example prints the employee's name in brackets, for instance @code{[Fred]}.
@example
(set-record-type-printer! employee-type
(lambda (record port)
(write-char #\[ port)
(display (get-employee-name record) port)
(write-char #\] port)))
@end example
@node Records

104
doc/ref/srfi-modules.texi
View file

@ -1862,110 +1862,12 @@ procedures easier. It is documented in @xref{Multiple Values}.
@node SRFI-9
@subsection SRFI-9 - define-record-type
@cindex SRFI-9
@cindex record
This SRFI is a syntax for defining new record types and creating
predicate, constructor, and field getter and setter functions. In
Guile this is simply an alternate interface to the core record
functionality (@pxref{Records}). It can be used with,
predicate, constructor, and field getter and setter functions. It is
documented in the ``Compound Data Types'' section of the manual
(@pxref{SRFI-9 Records}).
@example
(use-modules (srfi srfi-9))
@end example
@deffn {library syntax} define-record-type type @* (constructor fieldname @dots{}) @* predicate @* (fieldname accessor [modifier]) @dots{}
@sp 1
Create a new record type, and make various @code{define}s for using
it. This syntax can only occur at the top-level, not nested within
some other form.
@var{type} is bound to the record type, which is as per the return
from the core @code{make-record-type}. @var{type} also provides the
name for the record, as per @code{record-type-name}.
@var{constructor} is bound to a function to be called as
@code{(@var{constructor} fieldval @dots{})} to create a new record of
this type. The arguments are initial values for the fields, one
argument for each field, in the order they appear in the
@code{define-record-type} form.
The @var{fieldname}s provide the names for the record fields, as per
the core @code{record-type-fields} etc, and are referred to in the
subsequent accessor/modifier forms.
@var{predicate} is bound to a function to be called as
@code{(@var{predicate} obj)}. It returns @code{#t} or @code{#f}
according to whether @var{obj} is a record of this type.
Each @var{accessor} is bound to a function to be called
@code{(@var{accessor} record)} to retrieve the respective field from a
@var{record}. Similarly each @var{modifier} is bound to a function to
be called @code{(@var{modifier} record val)} to set the respective
field in a @var{record}.
@end deffn
@noindent
An example will illustrate typical usage,
@example
(define-record-type employee-type
(make-employee name age salary)
employee?
(name get-employee-name)
(age get-employee-age set-employee-age)
(salary get-employee-salary set-employee-salary))
@end example
This creates a new employee data type, with name, age and salary
fields. Accessor functions are created for each field, but no
modifier function for the name (the intention in this example being
that it's established only when an employee object is created). These
can all then be used as for example,
@example
employee-type @result{} #<record-type employee-type>
(define fred (make-employee "Fred" 45 20000.00))
(employee? fred) @result{} #t
(get-employee-age fred) @result{} 45
(set-employee-salary fred 25000.00) ;; pay rise
@end example
The functions created by @code{define-record-type} are ordinary
top-level @code{define}s. They can be redefined or @code{set!} as
desired, exported from a module, etc.
@unnumberedsubsubsec Non-toplevel Record Definitions
The SRFI-9 specification explicitly disallows record definitions in a
non-toplevel context, such as inside @code{lambda} body or inside a
@var{let} block. However, Guile's implementation does not enforce that
restriction.
@unnumberedsubsubsec Custom Printers
You may use @code{set-record-type-printer!} to customize the default printing
behavior of records. This is a Guile extension and is not part of SRFI-9. It
is located in the @nicode{(srfi srfi-9 gnu)} module.
@deffn {Scheme Syntax} set-record-type-printer! name thunk
Where @var{type} corresponds to the first argument of @code{define-record-type},
and @var{thunk} is a procedure accepting two arguments, the record to print, and
an output port.
@end deffn
@noindent
This example prints the employee's name in brackets, for instance @code{[Fred]}.
@example
(set-record-type-printer! employee-type
(lambda (record port)
(write-char #\[ port)
(display (get-employee-name record) port)
(write-char #\] port)))
@end example
@node SRFI-10
@subsection SRFI-10 - Hash-Comma Reader Extension